Plastic parts are extensively used in vehicle production. Molded polymeric fiber composites in particular are used in vehicle parts, such as liners and trims. These polymeric fiber composites often have performance specifications, such as the specifications associated with acoustical insulation. In constructs, such as interior vehicle parts, the weight of the molded part directly impacts upon the weight of the vehicle and ultimate efficiency of vehicle manufacture and operation along with the resistance of the molded part to deform or “sag”. Some fabrications of molded fibrous composite parts in the past have required multiple step molding, non-reusable components, and/or non-uniform preforms. Multilayered batt products, for instance, are known in which the constituent layers have different densities as a premolded material.
U.S. Pat. No. 7,137,477 B2 discloses sound absorbers made by predensifying separate base materials containing textile fiber material and binder with heat and pressure, and superimposing the fabrics and bonding them by action of heat and pressure without an adhesive or needle punching. One of the base materials alternatively can be predensified before the other binder containing base material is pasted onto it in the mold and densified by heat and pressure.
U.S. Pat. No. 5,079,074 discloses a dual density non-woven batt comprised of first and second batt layers that are fused together, and the first batt layer has a relatively high density and the second batt layer has a relatively low density before and after compression molding.
U.S. Pat. No. RE 39,010 discloses a lightweight acoustical system comprising an impermeable layer and an underlayment having a specific airflow resistance between about 2000 and about 5000 mks Rayls, comprising first and second fibrous layers bonded with a semi-permeable layer.
U.S. Pat. No. 4,131,664 discloses a multi-density fibrous acoustical panel comprising fibrous pad formed by incorporating suitable binding agents and a coextensive impervious membrane or film disposed intermediate of the face surface thereof.
U.S. Pat. No. 5,387,382 discloses a method for manufacturing an interior fitted part for a motor vehicle in which a staple fiber formed fabric of drawn polyethylene terephthalate matrix component and a polyester-containing binding component is subjected to precompaction and at least once during the process to an annealing process before molding.
U.S. Pat. No. 5,817,408 discloses a sound insulation structure comprising a low density layer that is high in sound-absorption coefficient and a high density layer that is a low spring constant layer. Each of the low and high density layers comprises first and second layers solely made of a first fiber and a second fiber respectively.
U.S. Pat. Nos. 6,572,723 B1 and 6,669,265 B2 disclose multilayer liners and insulators and processes for forming them in which an insulator precursor is disclosed that is formed with a polymer based blanket material formed from two composite layers having significantly different softening points or temperatures that are adhesively attached.